Systems and methods for frame tunnelling in wireless communications

ABSTRACT

Embodiments include systems and methods for frame tunneling in a wireless communications system comprising digital beam forming. Embodiments comprise a first and second frame control field with the second frame control field comprising a High Throughput Control (HTC) enabling field. If the HTC enabling field is enabled, then an HTC field is sent that announces a sounding frame and a type of channel estimation feedback expected from a receiving station.

FIELD

Embodiments are in the field of wireless communications. Moreparticularly, embodiments are in the field of communications protocolsbetween wireless transceivers.

BACKGROUND

A wireless communication system comprises at least one transmitter totransmit information over an RF (Radio Frequency) channel and at leastone receiver to receive the information from the RF channel. Moreparticularly, a wireless communication system may comprise two or morecommunication devices spaced apart, each device having a transceivercomprising a transmitter and a receiver. Typically, at least one devicetransceiver is able to transmit to and receive from the transceivers ofmultiple other devices. Some wireless communications systems utilizeDigital Beam Forming techniques to steer information into separatespatial channels.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the invention will become apparent upon reading the followingdetailed description and upon reference to the accompanying drawings inwhich like references may indicate similar elements:

FIG. 1 depicts an embodiment of an example wireless network comprising aplurality of communications devices, including multiple fixed or mobilecommunications devices.

FIG. 1A depicts a transfer protocol for establishing communicationsbetween wireless communication devices.

FIG. 1B depicts a tunneling frame including a first and second framecontrol field.

FIG. 1C depicts a second frame control field.

FIG. 1D depicts an example of a tunneling frame for implementing anAcknowledgment-High Throughput Control function.

FIG. 1E depicts an example of a tunneling frame for implementing a BlockAcknowledgment function.

FIG. 2 depicts a general flow of signal processing in a transceiver forOrthogonal Frequency Division Multiplexing (OFDM)-based broadbandcommunication in a wireless network.

FIG. 2A depicts an embodiment of an example QFDM suitable for use in atransmitter of the transceiver of FIG. 2.

FIG. 2B depicts an embodiment of an example OFDM suitable for use in areceiver of the transceiver of FIG. 2.

FIG. 3A depicts an example Digital Beam Former (DBF) suitable for use ina transmitter of the transceiver of FIG. 2.

FIG. 3B depicts an example DBF suitable for use in a receiver of thetransceiver of FIG. 2.

FIG. 4 depicts an example flowchart for constructing a tunneling frame.

DETAILED DESCRIPTION OF EMBODIMENTS

The following is a detailed description of embodiments of the inventiondepicted in the accompanying drawings. The embodiments are introduced insuch detail as to clearly communicate the invention. However, theembodiment(s) presented herein are merely illustrative, and are notintended to limit the anticipated variations of such embodiments; on thecontrary, the intention is to cover all modifications, equivalents, andalternatives falling within the spirit and scope of the appended claims.The detailed descriptions below are designed to make such embodimentsobvious to those of ordinary skill in the art.

Embodiments include systems and methods for frame tunneling in awireless communications system comprising digital beam forming.Embodiments comprise a first and second frame control field with thesecond frame control field comprising a High Throughput Control (HTC)enabling field. If the HTC enabling field is enabled, then an HTC fieldis sent that announces a sounding frame and a type of channel estimationfeedback expected from a receiving station.

FIG. 1 shows an embodiment of an example wireless network. Thisconfiguration comprises a first communications device 1010 that is wireline or wirelessly connected to a network 1000 such as the Internet or alocal intranet. Communication device 1010 may communicate wirelesslywith a plurality of communication devices 1030. For ease of reference,the communications devices 1010, 1030 are labeled as devices 0, 1, 2,and 3. A device 1030 may be a computer, laptop, notebook, cellularphone, PDA (Personal Digital Assistant), or other wireless-capabledevice. Thus, a communications device may be mobile or fixed.Communications device 1010 and devices 1030 each comprise a transceiver(RX/TX) 1014, 1034. Each transceiver comprises an RF transmitter and anRF receiver. Each RF transmitter impresses digital data onto an RFfrequency for transmission of the data by electromagnetic radiation. AnRF receiver receives electromagnetic energy at an RF frequency andextracts the digital data there from. FIG. 1 may depict a Multiple-InputMultiple-Output (MIMO) system. The wireless communication system of FIG.1 is intended to represent any of a wide variety of wireless systemswhich may include without limitation, NFC (Near Field Communications),WLAN (Wireless Local Area Network), WMAN (Wireless Metropolitan AreaNetwork), WiMAX (Worldwide Interoperability for Microwave Access),2.5-3G cellular, 3G RAN (Radio Access Network), 4G, RFID (RadioFrequency Identification), etc. In particular, in a WLAN, device 1010may represent the WLAN Access Point that controls a variety of differentWLAN devices compatible with different parts of the Institute forElectrical and Electronics Engineers (IEEE) standard 802.11, including802.11a, 802.11b, and 802.11g, as well 802.11n. Similarly, devices 1030may comply with different ones of these standards.

In one embodiment, communications device 1010 comprises a Digital BeamFormer (DBF) 1016. DBF 1016 transforms information signals into signalsto be applied to elements of an antenna array 1022. Antenna array 1022is an array of individual, separately excitable antenna elements. Thesignals applied to the elements of antenna array 1022 cause it toradiate a plurality of spatial channels. Each spatial channel so formedmay carry information to one or more of communication devices 1030.Similarly, a communication device 1030 comprises a transceiver 1032 toreceive and transmit signals from and to device 1010. Transceiver 1032may also comprise an antenna array 1042 and a DBF 1036. In parallel withDigital Beam Forming, transceiver 1032 is capable of transmitting andreceiving signals in accordance with IEEE standards 802.11a and 802.11g.

Communication devices 1010, 1030 also comprise a frame builder 1012,1032, respectively. Frame builder 1012, 1032 constructs frames thatprefix data to be transmitted over the RF channel. These frames may bestored in Direct Random Access Memory (DRAM) 1011, 1031. A purpose of aframe is to establish and maintain synchronized communications betweenthe transmitting device and the receiving device. Each frame builder maysupply a High Throughput Control (HTC) field 1013, 1033. The HTCprovides a bit sequence that announces the transmission of a soundingframe that enables a receiver of the sounding frame to estimate thechannel between the receiver and transmitter of the HTC. The HTC alsospecifies a type of feedback expected from the receiver. In one mode ofoperation, the type of feedback is an estimate of a channel matrix,wherein another type of feedback is a steering matrix for beam steeringof information into a plurality of substantially independent spatialchannels. A main difference between these two types of feedback is thatthe channel matrix is more precise but takes longer to transmit back tothe transmitter, whereas a steering matrix is shorter but takes longerto compute by the receiver.

FIG. 1A illustrates the operation of one of the functions of a frame. Toestablish communications, a transmitter transmits a control frame. Thecontrol frame comprises a Request To Send (RTS) field that is receivedby a receiver. The control frame also comprises an address field and aduration field (not shown in FIG. 1A). The address field indicates towhich receiver the transmission is intended. The duration fieldcomprises a Network Allocation Vector (NAV) that indicates the durationof time reserved for the transmission. After the RTS signal is sent, butbefore the data of the transmission is sent, the transmitter waits toreceive a Clear To Send (CTS) signal from the receiver. If the CTS isnot received within a short period of time, the intended transmission istemporarily abandoned and a new RTS signal may be sent later. Once theCTS signal is received, the transmitter sends the data during theduration of the NAV, as shown in FIG. 1A. If the data is successfullyreceived, the receiver transmits an acknowledgment (ACK) signal to thetransmitter. If an ACK signal is not received, the source station mayimmediately schedule a retransmission.

The methodology depicted in FIG. 1A is used in wireless systems thatinclude Wireless Local Area Networks (WLAN) and Wireless MetropolitanArea Networks (WMAN) that are compliant with Standards 802.11,promulgated by the Institute of Electrical and Electronics Engineers(IEEE 802.11). The standards encompass legacy systems that comply withthe existing IEEE 802.11 standard, and existing supplemental standardssuch as 802.11a, 802.11b and 802.11g. These standards do not specifydigital beam forming. However, a new supplemental standard beingdeveloped and designated IEEE 802.11n does provide specifications fordigital beam forming. In particular, the standard 802.11n specifies thata High Throughput Control (HTC) field be transmitted as part of a framethat prefixes the data to be transmitted. However, a simpleconcatenation of the HTC with the control frame renders a legacy stationunable to assert the NAV during the duration field because the format nolonger complies with legacy standards for frame format. Thus, a newframe structure is needed for High Throughput Control. Accordingly,frame builder 1012, 1032 provides a second frame control field 1015,1035, as will be explained subsequently.

FIG. 1B shows an embodiment of a tunneling frame format built by framebuilder 1012, 1032. A first frame control field is provided thatconforms to the current state of the new 802.11n standard underdevelopment. The first frame control field may provide a protocolversion field to specify the applicable standard. A type field specifieswhether the frame is a management, control or data frame. In the presentcase, for transmission of HTC, the type is control. Also, there is asubtype field to specify the function of the frame. In the present case,the subtype is tunnel. The duration field that follows the first framecontrol field specifies the duration of this transmission. The addressfield specifies the address of the intended receiver or receivers forthis transmission.

Following the address field is a second frame control field 1015, 1035.FIG. 1C shows a more detailed view of a second frame control field. Thesecond frame control field comprises a byte count field that enablesearly detection of error in transmission. The following field is asubtype field which specifies the functionality of the frame. A subtypemay be, for example, an ACK (acknowledgement), RTS, CTS, BA (blockacknowledgement), or other subtype. Following the subtype field is anHTC enable field. When this field is enabled (logic level 1, forexample), the HTC field will immediately follow. Subsequent to thesecond frame control field is a Frame Check Sequence (FCS) thatcomprises a 32 bit cyclic redundancy sequence used to determine if theframe is received correctly.

FIG. 1D shows an example of a frame for transmitting the HTC used forchannel estimation by a receiver of the frame. A first frame control isof type control and of subtype tunnel. Following the first frame controlis the duration and address fields. In this example, the byte countfield of the second frame control is 20. The subtype is ACK and HTCenable is enabled. Following the second frame control is the HTC field,followed by the Frame Check Sequence (FCS). FIG. 1E depicts a frame forwhen the subtype of the second frame control is BA (BlockAcknowledgement) and the HTC enable field is disabled. This demonstratesthat the second frame control field may be used for multiple purposesalready defined and yet to be defined in 802.11n. In this example, theBA field within the second frame control field provides agreementbetween the transmitter and receiver to transmit blocks of data frames.The BA control field provides an identity of this agreement. Theaddress2 field contains the transmitter address. The SSN (StartingSequence Number) field is the sequence number of the first data framefor which the BA is sent. The Bitmap field is a sequence of bits, onefor each frame sent in the block. When set to 1, a bit of the bitmapfield indicates that the corresponding data frame is receivedsuccessfully. When set to 0, this indicates that the corresponding frameis lost.

Embodiments thus provide a method for frame tunneling with backwardcompatibility with legacy systems and with High Throughput Control forsystems comprising digital beam forming. This tunneling approach candeliver Network Allocation Vectors (NAV) using transmission rates andwaveforms already used by existing legacy systems, as well as deliveringNAVs using rates and waveforms of high throughput networks such as thosefor 802.11n. One subtype is used to deliver different frames, therebypreserving the limited range of applicable subtypes. Thus, differentframes can be submitted that include modified frames already defined inthe current state of 802.11n, as well as new frames. Including a bytecount field increases the level of reliability of the frame at earlystages of decoding. Embodiments further allow one to submit frames withone address field with low overhead because the second frame controlfield follows the address field.

Note that the methodology of frame tunneling described herein appliesnot only to frames that are of type “control” but of type “data” and“management” as well as other types that may be defined by an applicablestandard. Note also that apart from announcing a sounding frame and atype of channel estimation feedback, the HTC field may comprise otherinformation instead or as well. For example, the HTC field may comprisea field that requests from a receiving station a modulation and codescheme. The HTC field may comprise a field that requests from areceiving station antenna selection information to select certainelements of the antenna array of the transmitting station fortransmission to the receiving station. The HTC field may comprise areverse direction field that allows the transmitter to temporarilydelegate its transmitter rights to a receiving station for betterutilization of link capacity. Also note that the second frame controlfield may comprise, in addition to or instead of, the byte count field,a transmission rate field specifying a data transmission rate for earlyerror detection by the receiving station.

Accordingly, present embodiments provide a communication device,comprising a frame builder to provide a medium access frame comprising aframe control field and a high throughput control (HTC) field. The HTCfield announces a subsequent transmission of a sounding frame and thetype of feedback expected from a receiver of the sounding frame. Theframe builder may be implemented in hardware by an application specificintegrated circuit, or may be implemented in firmware. Embodimentsfurther provide a transceiver with a digital beam former and an array ofantennas to transmit the frame and a sounding frame through a spatialchannel to a receiving communication device.

FIG. 2 shows a more detailed view of a general flow of example signalprocessing in a transceiver 200. Transceiver 200 comprises a receiver204 and a transmitter 206. Transmitter 206 may comprise one or more ofan encoder 208, a modulator 210, an OFDM 212, and a DBF 214. Receiver204 may comprise one or more of a DBF 220, an OFDM 222, a demodulator224 and a decoder 226. Each of these components of transceiver 200 andtheir functions will now be described.

Encoder 208 of transmitter 206 receives data destined for transmissionfrom a processor core 202. Processor core 202 may present data totransceiver 200 in blocks such as bytes of data. In particular,processor core 202 comprises a frame builder to construct and send tothe transceiver medium access frames. Encoder 208 encodes the data usingany one of a number of algorithms now known or to be developed. Encodingmay be done to achieve one or more of a plurality of different purposes.For example, coding may be performed to decrease the average number ofbits that must be sent to transfer each symbol of information to betransmitted. Coding may be performed to decrease a probability of errorin symbol detection at the receiver. Thus, an encoder may introduceredundancy to the data stream. Adding redundancy increases the channelbandwidth required to transmit the information, but results in lesserror, and enables the signal to be transmitted at lower power. Encodingmay also comprise encryption for security.

One type of encoding is block encoding. In block encoding, the encoderencodes a block of k information bits into corresponding blocks of ncode bits, where n is greater than k. Each block of n bits from theencoder constitutes a code word in a set of N=2^(k) possible code words.An example of a block encoder that can be implemented is a Reed-Solomonencoder, known by those skilled in the art of encoding. Another type ofencoding is linear convolutional encoding. The convolutional encoder maybe viewed as a linear finite-state shift register with an outputsequence comprising a set of linear combinations of the input sequence.The number of output bits from the shift register for each input bit isa measure of the redundancy in the code. Thus, different embodiments mayimplement different encoding algorithms.

Modulator 210 of transmitter 206 receives data from encoder 208. Apurpose of modulator 210 is to transform each block of binary datareceived from encoder 208 into a unique continuous-time waveform thatcan be transmitted by an antenna upon up-conversion and amplification.Modulator 210 impresses the received data blocks onto a sinusoid of aselected frequency. More specifically, modulator 210 maps the datablocks into a corresponding set of discrete amplitudes of the sinusoid,or a set of discrete phases of the sinusoid, or a set of discretefrequency shifts relative to the frequency of the sinusoid. The outputof modulator 210 is a band pass signal.

In one embodiment, modulator 210 maps a sequence of binary digits into aset of discrete amplitudes of a carrier frequency. This is called PulseAmplitude Modulation (PAM). Quadrature Amplitude Modulation (QAM) isattained by impressing two separate k-bit symbols from the informationsequence onto two quadrature frequencies, cos(2πθt) and sin(2πƒt).

In another embodiment, modulator 210 maps the blocks of data receivedfrom encoder 208 into a set of discrete phases of the carrier to producea Phase-Shift Keyed (PSK) signal. An N-phase PSK signal is generated bymapping blocks of k=log₂ N binary digits of an input sequence into oneof N corresponding phases θ=2π(n−1)/n for n a positive integer less thanor equal to N. A resulting equivalent low pass signal may be representedas${u(t)} = {\sum\limits_{n = 0}^{\infty}{{\mathbb{e}}^{j\quad\theta_{n}}{g\left( {t - {nT}} \right)}}}$where g(t−nT) is a basic pulse whose shape may be optimized to increasethe probability of accurate detection at a receiver by, for example,reducing inter-symbol interference. Inter-symbol interference resultswhen the channel distorts the pulses. When this occurs adjacent pulsesare smeared to the point that individual pulses are difficult todistinguish. A pulse shape may therefore be selected to reduce theprobability of symbol misdetection due to inter-symbol interference.

In yet another embodiment, modulator 210 maps the blocks of data from aninformation sequence received from encoder 208 into a set of discretefrequency shifts to produce a Frequency-Shift-Keyed (FSK) signal. Aresulting equivalent low pass signal may be represented as:${u(t)} = {\sum\limits_{n = 0}^{\infty}{{\exp\left( {j\quad\pi\quad\Delta\quad{ftI}_{n}} \right)}{g\left( {t - {nT}} \right)}}}$where I_(n) is an odd integer up to N−1 and Δƒ is a unit of frequencyshift. Thus, in an FSK signal, each symbol of an information sequence ismapped into one of N frequency shifts.

Persons of skill in the art will recognize that the mathematicalequations discussed herein are illustrative, and that differentmathematical forms may be used to represent the pertinent signals. Also,other forms of modulation that may be implemented in modulator 210 areknown in the art.

The output of modulator 210 may be up-converted to a higher carryingfrequency. Or, modulation may be performed integrally withup-conversion. Shifting the signal to a much higher frequency beforetransmission enables use of an antenna array of practical dimensions.That is, the higher the transmission frequency, the smaller the antennacan be. Thus, an up-converter multiplies the modulated waveform by asinusoid to obtain a signal with a carrier frequency that is the sum ofthe central frequency of the waveform and the frequency of the sinusoid.The operation is based on the trigonometric identity:${\sin\quad A\quad\cos\quad B} = {\frac{1}{2}\left\lbrack {{\sin\left( {A + B} \right)} + {\sin\left( {A - B} \right)}} \right\rbrack}$The signal at the sum frequency (A+B) is passed and the signal at thedifference frequency (A−B) is filtered out. Thus, a band pass filter isprovided to ideally filter out all but the information to betransmitted, centered at the carrier (sum) frequency.

The output of modulator 210 is fed to an Orthogonal Frequency DivisionMultiplexer (OFDM) 212. OFDM 212 impresses the modulated data frommodulator 210 onto a plurality of orthogonal sub-carriers. A blockdiagram of one embodiment of an OFDM 212 is shown in FIG. 2A. A serialbit stream is converted to blocks of n bits of data in parallel by aserial-to-parallel converter 250. Optionally, each bit is modulated inparallel by a modulator 252, instead of, or in addition to themodulation provided by modulator 210. Then, an inverse discrete Fouriertransform (DFT), e.g. a Fast Fourier Transform (FFT), is performed onthe data by inverse FFT 254. This impresses the data onto multipleorthogonal sub-carriers. Then, the data may be converted to a serialstream of data of different channels by a parallel to serial converter256.

Returning to FIG. 2, the output of OFDM 212 is fed to Digital BeamFormer (DBF) 214. Digital beam forming techniques are employed toincrease the efficiency and capacity of a wireless system. Generally,digital beam forming uses digital signal processing algorithms thatoperate on the signals received by, and transmitted from, an array ofantenna elements to achieve enhanced system performance. For example, aplurality of spatial channels may be formed and each spatial channel maybe steered independently to maximize the signal power transmitted to andreceived from each of a plurality of user terminals. Further, digitalbeam forming may be applied to minimize multi-path fading and to rejectco-channel interference.

The problem to be solved by digital beam forming may be stated generallyas the problem of separating a set of L information signals, y, that aresuperimposed and received by an N-element antenna array as a set of Nsignals, x. Conversely, digital beam forming is employed to solve theproblem of combining a set of L information signals, y, to form a set ofN signals, x, to be transmitted by the N elements of the antenna array.The desired information signals, y, may be obtained from a matrixmultiplication on the received signals, x:y=Uxwhere U is a matrix determined by computational methods. Similarly, aset of signals, x, to be transmitted by the array may be obtained from amatrix multiplication on the information signals, y:x=Vywhere V is also a matrix determined by computational methods. Thematrices U and V are chosen to separate out at least one of theinformation signals of y from a received vector of signals x. Note thatthe matrices U and V are not inverses of each other since the requiredbeam steering for transmission and reception are generally not the same.

FIG. 3A shows a multiple beam former 3000 for transmitting L beams froman N-element antenna array. L information signals, y₁ through y_(L), areinput in parallel to power dividers 3002. Each power divider 3002divides the received information signal into N parallel channels. At theoutput of a power divider, the signal in each of the N channels ismultiplied by a different weight, W¹ _(n), each weight being an entry inthe matrix V. The resultant products are multiplexed to a plurality ofcombiners 3004. The output of the combiners (e.g., summers) 3004 are thesignals x₁ to x_(N). Each signal x_(n) is fed to a different one of theN antenna array elements of an antenna array 218.

FIG. 2 also shows diplexers 216 connected to antenna array 218. Thus, inthis embodiment, a single antenna array is used for both transmissionand reception. When transmitting, the signal passes through diplexers216 and drives the antenna with the up-converted information-bearingsignal, x. During transmission, the diplexers prevent the signals to betransmitted from entering receiver 204. When receiving, informationbearing signals received by the antenna array pass through diplexers 216to deliver the signal from the antenna array to receiver 204. Thediplexer then prevents the received signals from entering transmitter206. Thus, diplexers 216 operate as switches to alternately connect theantenna array elements to the receiver and the transmitter.

Antenna array 218 radiates the information bearing signals into atime-varying, spatial distribution of electromagnetic energy that can bereceived by an antenna of a receiver. The receiver can then extract theinformation of the received signal. An array of antenna elements canproduce multiple spatial channels that can be steered to optimize systemperformance. Reciprocally, multiple spatial channels in the radiationpattern at a receive antenna can be separated into different spatialchannels. Thus, a radiation pattern of antenna array 218 may be highlyselective. Antennas 218 may be implemented using existing printedcircuit board metallization technology. Microstrips, striplines,slotlines, and patches, for example, are all candidates for antennas218.

FIG. 2 also shows an embodiment of a receiver 204 for receiving,demodulating, and decoding information bearing signals. The receivedsignals are fed from antenna elements 218 to a Digital Beam Former (DBF)220. DBF 220 transforms N antenna signals into L information signals.FIG. 3B shows a functional diagram of DBF 220, 3010 for determininginformation signals y from received signals x. The N received signals,x, are each fed to power dividers 3012. The outputs of power dividers3012 are multiplexed among a set of combiners 3014. Each input to acombiner is multiplied by a weight, W¹ _(n), each weight being an entryin the matrix U, for computation of y=Ux.

The output of DBF 220 is fed to Orthogonal Frequency DivisionMultiplexer (OFDM) 222. OFDM 222 extracts signal information from theplurality of subcarriers onto which information bearing signals aremodulated. FIG. 2B shows a block diagram of OFDM 222. First, asequential stream of data is converted to parallel 260. Then, a discreteFourier transform (DFT) such as, e.g., a Fast Fourier Transform (FFT)262 is performed to extract the signal information from thesub-carriers. In one embodiment, demodulation 264 is performed inparallel on the output data of the FFT. In another embodiment,demodulation is performed separately by a separate demodulator 224.Accordingly, in one embodiment, the OFDM processed signals are convertedto a serial data stream 266 and input to demodulator 224.

Demodulator 224 demodulates the received signal. Demodulation is theprocess of extracting information content from the received signal toproduce an un-demodulated information signal. The method of demodulationdepends on the method by which the information is modulated onto thereceived carrier signal. Thus, for example, if the modulation is PSK,demodulation involves phase detection to convert phase information to abinary sequence. Demodulation provides to the decoder a sequence of bitsof information. Decoder 226 decodes the received binary data blocks fromdemodulator 224 and transmits the decoded information to processor core202.

Thus, embodiments include a wireless-capable unit, comprising a framebuilder. A transmitter coupled to the frame builder comprises a digitalbeam former and an antenna array to transmit a frame from the framebuilder. The frame comprises a first frame control field and a secondframe control field followed by a high throughput control (HTC) field.The HTC field announces a subsequent sounding frame and specifies a typeof channel estimation feedback expected from a receiving station of thetransmitted frame. A receiver of the wireless unit receives channelestimation feedback from the receiving station of the transmitted frame.The channel estimation feedback may comprise an estimate of a channelmatrix or may comprise a beam steering matrix.

Persons of skill in the art will recognize that a transceiver willcomprise numerous additional functions not shown in FIG. 2. Thus, atransceiver will comprise a Direct Random Access Memory (DRAM), areference oscillator, filtering circuitry, synchronization circuitry,possibly multiple frequency conversion stages and multiple amplificationstages, etc. Further, some of the functions shown in FIG. 2 may beintegrated. For example, digital beam forming may be integrated withorthogonal frequency division multiplexing. Thus, FIG. 2 shows a generalflow of signal processing in a transceiver. Actual implementations mayvary. For example, not all embodiments may apply OFDM.

The RF channel between communications devices has a transfer function:H=USV^(T)Where U and V are unitary steering matrices and S is a rectangularmatrix whose diagonal elements are real and non-negative and whoseoff-diagonal elements are zero. If the channel matrix H can bedetermined, the matrices U and V can be computed using the method ofSingular Value Decomposition (SVD). Accordingly, a transmitting stationmay transmit a sounding frame to a receiving station to enable thereceiving station to estimate the channel between the transmittingstation and the receiving station. Before sending the sounding frame,the HTC enabling field of the second frame control field of the mediumaccess control field is enabled and the HTC frame is transmitted. TheHTC frame announces the transmission of the sounding frame and specifiesthe type of feedback expected from the receiving station.

Thus, embodiments provide for spatial channel steering in a wirelesssystem. In one embodiment, a receiver of a first communications deviceestimates a channel matrix from a sounding frame received from a secondtransmitting device. The first device may decompose the channel matrixto obtain a spatial channel matrix, H. In one embodiment, the spatialchannel matrix is transmitted to the second device. Within the seconddevice, the spatial channel matrix is resolved into a steering matrix Vthat is applied to information signals to produce substantiallyindependent spatial channels. In another mode of operation, the receiverof the first device computes the steering matrix V for beam steering ofinformation into a plurality of substantially independent spatialchannels. The receiver of the first device then transmits the steeringmatrix to the second device. A main difference between these two typesof feedback is that the channel matrix is more precise but takes longerto transmit back to the transmitter, whereas a steering matrix isshorter but takes longer to compute by the receiver. The HTC field inthe frame following the second frame control field indicates which modeof operation is performed by the receiving device.

FIG. 4 shows an example flowchart 400 of an embodiment for building acontrol frame according to embodiments described herein. To designatethat the frame is for control, the systems sets the type of the firstframe control field to “control” (element 402). To designate that thecontrol frame is a tunneling frame, the system sets the type of thefirst frame control field to “tunnel” (element 404). The system alsosets the subtype of the second frame control field (element 406). Thissubtype designates the function of the control frame and may be ofsubtype RTS, CTS, ACK, BA or other subtype defined in the relevantstandard or to be defined by a standard such as IEEE 802.11.n The systemdetermines if an HTC field is to be transmitted (element 408). If not,the system disables the HTC enable field of the second frame controlfield (element 410) and the system constructs the remainder of thecontrol frame accordingly (element 416). If the system determines thatan HTC field is to be transmitted, the system enables the HTC enablefield (element 412). The system also sets the value of the HTC fielditself to announce the sounding frame transmission and the type offeedback expected from the receiving station (element 414). The systemfurther constructs the remainder of the control frame including theframe check sequence (element 416).

Thus, embodiments may comprise a method for medium access control forachieving high throughput in a wireless communications system employingbeam steering. One such method comprises providing a first frame controlfield of a subtype equal to tunnel. A second frame control field isprovided comprising a high throughput control (HTC) enable field toindicate whether a subsequent field comprises an HTC field to announcetransmission of a sounding frame for channel estimation. If the HTCenabling field is enabled, an HTC field is provided to announcetransmission of a sounding frame for channel estimation.

Some embodiments of the invention are implemented as a program productfor use with an embedded processor such as processor core 202 of FIG. 2.The program product could be used on other computer systems orprocessors. The program(s) of the program product defines functions ofthe embodiments (including the methods described herein) and can becontained on a variety of signal-bearing media. Illustrativesignal-bearing media include, but are not limited to: (i) informationpermanently stored on non-writable storage media (e.g., read-only memorydevices within a computer such as CD-ROM disks readable by a CD-ROMdrive); (ii) alterable information stored on writable storage media(e.g., floppy disks within a diskette drive or hard-disk drive); and(iii) information conveyed to a computer by a communications medium,such as through a computer or telephone network, including wirelesscommunications. The latter embodiment specifically includes informationdownloaded from the Internet and other networks. Such signal-bearingmedia, when carrying computer-readable instructions that direct thefunctions of the present invention, represent embodiments of the presentinvention.

In general, the routines executed to implement the embodiments of theinvention, may be part of an operating system or a specific application,component, program, module, object, or sequence of instructions. Thecomputer program of the present invention typically is comprised of amultitude of instructions that will be translated by the native computerinto a machine-accessible format and hence executable instructions.Also, programs are comprised of variables and data structures thateither reside locally to the program or are found in memory or onstorage devices. In addition, various programs described hereinafter maybe identified based upon the application for which they are implementedin a specific embodiment of the invention. However, it should beappreciated that any particular program nomenclature that follows isused merely for convenience, and thus the invention should not belimited to use solely in any specific application identified and/orimplied by such nomenclature.

Thus, another embodiment of the invention provides a machine-accessiblemedium containing instructions effective, when executing by a machine,to cause the machine to perform a series of operations for tunnelingframe construction. The operations comprise generating a first framecontrol field to designate a frame as a tunneling frame. The operationsfurther comprise generating a second frame control field comprising ahigh throughput control (HTC) enabling field to indicate whether asubsequent field shall comprise an HTC field to announce transmission ofa sounding frame for channel estimation. The operations also comprisegenerating an HTC field to announce transmission of a sounding frame forchannel estimation if the HTC enabling field is set to enable.

The present invention and some of its advantages have been described indetail for some embodiments. It should be understood that variouschanges, substitutions and alterations can be made herein withoutdeparting from the spirit and scope of the invention as defined by theappended claims. An embodiment of the invention may achieve multipleobjectives, but not every embodiment falling within the scope of theattached claims will achieve every objective. Moreover, the scope of thepresent application is not intended to be limited to the particularembodiments of the process, machine, manufacture, composition of matter,means, methods and steps described in the specification. One of ordinaryskill in the art will readily appreciate from the disclosure of thepresent invention that processes, machines, manufacture, compositions ofmatter, means, methods, or steps, presently existing or later to bedeveloped are equivalent to, and fall within the scope of, what isclaimed. Accordingly, the appended claims are intended to include withintheir scope such processes, machines, manufacture, compositions ofmatter, means, methods, or steps.

1. A method for medium access control for achieving high throughput in awireless communications system employing beam steering, comprising:generating a first frame control field to designate a frame as atunneling frame; generating a second frame control field comprising ahigh throughput control (HTC) enabling field to indicate whether asubsequent field shall comprise an HTC field to announce transmission ofa sounding frame for channel estimation; and generating an HTC field toannounce transmission of a sounding frame for channel estimation if theHTC enabling field is set to enable.
 2. The method of claim 1, whereinthe first and second frame control fields are part of a control frame ofa type designated as control.
 3. The method of claim 1, wherein thefirst and second frame control fields are part of a control frame of atype designated as other than control.
 4. The method of claim 1, whereingenerating the second frame control field further comprises generating abyte count field to enable early error detection.
 5. The method of claim1, wherein generating the second frame control field further comprisesgenerating a transmission rate field to enable early error detection. 6.The method of claim 1, wherein generating the second frame control fieldfurther comprises generating a subtype field to designate a framefunction.
 7. The method of claim 1, wherein generating the HTC fieldfurther comprises generating a request for modulation and code scheme.8. The method of claim 1, wherein generating the HTC field furthercomprises generating a request for antenna element selection.
 9. Themethod of claim 1, wherein generating the HTC field further comprisesgenerating a reverse direction request.
 10. The method of claim 1,wherein the HTC enabling field is disabled to permit implementation of aframe function other than for HTC field transmission.
 11. The method ofclaim 1, wherein the second frame control field designates a Request toSend function.
 12. The method of claim 1, wherein the second framecontrol field designates a Block Acknowledgment function.
 13. The methodof claim 1, wherein the second frame control field designates anAcknowledgment function.
 14. The method of claim 1, wherein the secondframe control field designates a Clear to Send function.
 15. The methodof claim 1, wherein the second frame control field designates a BlockAcknowledgment Request function.
 16. A device for wirelesscommunication, comprising: a frame builder to provide a medium accessframe comprising a first and second frame control field and a highthroughput control (HTC) field; and a transmitter with a digital beamformer and an array of antennas to transmit the frame and a soundingframe through a spatial channel to a receiving communication device. 17.The device of claim 16, wherein the transmitter further comprises anorthogonal frequency division multiplexer to modulate informationsignals onto orthogonal sub-carriers.
 18. The device of claim 16,further comprising a receiver to receive channel estimation feedbackfrom the receiving communication device.
 19. The device of claim 16,wherein the sounding frame can enable the receiving communication deviceto perform channel estimation.
 20. A device for wireless communication,comprising: Direct Random Access Memory (DRAM) connected to a framebuilder; a frame builder to generate a frame comprising a first framecontrol field to specify that the generated frame is a tunneling frame,comprising a second frame control field to specify a function of theframe, and optionally comprising a high throughput control field thatcan announce a subsequent sounding frame and can specify a type ofchannel estimation feedback to be received from a receiving station ofthe transmitted frame a transmitter comprising a digital beam former andan antenna array to transmit the frame from the frame builder and totransmit the sounding frame; and a receiver to receive channelestimation feedback from the receiving station of the transmitted frame.21. The device of claim 20, further comprising within the transmitter amodulator for modulating information onto orthogonal sub-carriers. 22.The device of claim 20, further comprising within the receiver ademodulator for demodulating information modulated onto orthogonalsub-carriers.
 23. The device of claim 20, wherein the second framecontrol field further comprises a byte count field to enable early errordetection by the receiving station.
 24. The device of claim 20, whereinthe second frame control field further comprises a subtype field todesignate a frame function.
 25. A machine-accessible medium containinginstructions for generating a medium access frame in a wireless, digitalbeam forming system, which, when the instructions are executed by amachine, cause said machine to perform operations, comprising:generating a first frame control field to designate a frame as atunneling frame; generating a second frame control field comprising ahigh throughput control (HTC) enabling field to indicate whether asubsequent field shall comprise an HTC field to announce transmission ofa sounding frame for channel estimation; and generating an HTC field toannounce transmission of a sounding frame for channel estimation if theHTC enabling field is set to enable.
 26. The machine accessible mediumof claim 25, wherein the operations further comprise generating a bytecount field to enable early error detection.
 27. The machine accessiblemedium of claim 25, wherein the operations further comprise generating asubtype field to designate a frame function.
 28. The machine accessiblemedium of claim 25, wherein the operations further comprise disablingthe HTC enabling field to permit implementation of a frame functionother than for HTC field transmission.
 29. The machine accessible mediumof claim 25, wherein the operations further comprise generating asounding frame to enable a receiving communication device to performchannel estimation.